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Let's assume that humans can now run 40 mph and the human body can handle it. I know and understand that this is not feasible, but let's just play pretend. Naturally people would have all kinds of fun, but as we all know most people are wild, panicky idiots. I imagine that there would be millions of people who have accidents such as:

  • Head on (other head) collision
  • Not stopping in time for actual traffic
  • Running into walls

Obviously this is a problem, as it's not a car but an ability the government can't just take it away. So, what is the cheapest solution for keeping people alive in this scenario?


Okay, so this question caused a lot of problems (and has attracted a few people new to worldbuilding) as I have not put enough detail to fully answer it.

  1. The biggest problem is the whole "humans would evolve to counteract this" argument. What I meant is what if humans suddenly gained this ability.
  2. To White Fang's question; lets assume that a fit human can keep up this speed for around an hour before they need a break.
  3. To Aarthew III's question; as they now have this new ability their reflexes would be the same.
  4. While I do agree with Twelfth, running to and from places would be more common, that is not the point of this question.

Hopefully this has cleared some confusion.

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closed as primarily opinion-based by Aify, XandarTheZenon, dan1111, JDługosz, type_outcast Mar 28 at 13:11

Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise.If this question can be reworded to fit the rules in the help center, please edit the question.

You don't. Darwin will have his way. – Separatrix Mar 22 at 19:03
I don't see this as a problem. People can jump off buildings. The few that do, die; the many that don't, carry on. – Mikey Mar 22 at 19:05
I think you should consider the implications (evolution, societal, and technological) of most humans being able to run that fast on a whim (without special training and a lot of effort). Humans would probably not look the way we do today, and warfare, sports, etc would be considerably different. – AndreiROM Mar 22 at 19:38
Suddenly, this company becomes incredibly rich. – cobaltduck Mar 22 at 19:58
Don't you have the same problem with real humans? The fastest human (currently) runs 27.8 mph; when I was in high school, I could run close to 20 mph. Even at those speeds, you could do some serious damage if you ran into a brick wall or hit another person head on. – fool4jesus Mar 22 at 22:20

16 Answers 16

up vote 64 down vote accepted

Taking this to be an evolved trait not suddenly given. (The edit has changed the rules on this and largely invalidated this answer)

Three factors are key here.

  1. Evolution
  2. Culture
  3. Speed


Having developed with this ability, there's no reason why people should be particularly dangerous with it. Horses don't crash headlong into each other, why should humans.


Each region or cultural group would have a solution to seeing someone running headlong towards them. It would normally consist of slowing down and moving left. This would mean that collisions are highly unlikely to happen. You'll also find that with the ability to run faster than horses, we wouldn't have the same requirements for personal transportation. Apart from haulage you'd find very little of what we'd call normal day to day traffic. Why sit in the city rush hour when you can just run and get there in a fraction of the time. I'm not talking about running flat out all the way here, you could just jog along at 20mph and you'd still leave the 8mph average of the city far behind you.


40mph isn't all that fast. The speed limit on single track roads (only wide enough for a single vehicle, often with high banks or ditches on both sides) in the UK is 60mph and we can cope with that without kinaesthesia. 40 mph is well within human reaction and reflex times, and with a cultural adaptation to traffic control, 80mph relative to oncoming persons is also not a problem.

As anyone who has worked in customer service will tell you, people are stupid. There's no helping some people, but on the whole people will be fine. As for the rest, Darwin can have them.

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Comments are not for extended discussion; this conversation has been moved to chat. – HDE 226868 Mar 23 at 23:27
"40mph isn't all that fast." Thank you!! Now if only you could convince all the road hogs everywhere of that! :) – Deepak Mar 26 at 0:58
40mph is very fast for a human; the world record 100m dash equates to 23.4mph. Compare that to the 20mph school zone restriction, which is set because collisions with pedestrians at 25mph lead to serious injuries and collisions at 40mph lead to fatalities. Imagine tripping when running at 40mph! – Adam Katz Mar 26 at 1:54
@AdamKatz that's all been covered already in the comments moved to chat. – Separatrix Mar 26 at 8:48
up vote 142 down vote

People would likely use a portable, protective encasement when traveling at or near their maximum speed.

Here is a possible prototype:

enter image description here

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+1 for the ingenious answer. – TrEs-2b Mar 23 at 23:34
I'm so freaking jealous that I didn't think of this. If I could give this a +10 I would. – The Anathema Mar 23 at 23:46
I'd upvote a million times if I could – slebetman Mar 24 at 8:14
This is amazing. I mean, there's hardly any content to the answer except Mr Flintstone... – Daniel Mar 24 at 15:24
You sir are a genius.. give this man more points... – TheAlbear Mar 24 at 16:57

The premise of the question is faulty.

People are not so stupid that they would run around and go bumping into things at random. The vast majority of the human race already successfully accomplishes tasks with equivalent level of risk to what you describe (driving a car, riding a bike, crossing a busy street, etc.).

Or look at it another way: the level of intelligence required to successfully navigate at high speeds is far lower than human intelligence. You typically don't see animals crashing into walls, even though some are much faster than your 40mph humans (cheetahs and falcons, for example).

Update: the edit to the question, that humans gained the ability suddenly, doesn't change this point.

Sure, suddenly being able to run really fast would create teething problems, including bad accidents as people learned to use their new found ability. However, the point remains that human intelligence is far more than needed to control this ability.

It wouldn't be the "stupid people" dying from accidents but a random sample from across the human spectrum.

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Indeed. People who can run 40 mph would learn when to stop. Just like how toddlers learn to be careful running around the house. – jpmc26 Mar 23 at 21:37
The question was edited to indicate that this speed was something abruptly gained, rather than something we learned to use as children (when we did go bumping into things at random). You may wish to either edit your answer, as it no longer addresses the question very directly. – nitsua60 Mar 24 at 15:59
But the lack of reaction time changing is relevant. – tox123 Mar 25 at 20:37
The question states that most people are stupid. And they are - just think how many car accidents happen every day. Accidens happen when people take risks. Running to an intersection assuming there wont be anyone else running across, and so on. – diynevala Mar 25 at 21:33
@tox123 agreed, much agreed. – Aarthew III Mar 27 at 3:58

Let's slow down time.

I'm going to borrow a second ability from other animals, like the fly or hummingbird.

According to the paper Metabolic rate and body size are linked with perception of temporal information animals utilise a feature that's very much like slowed down time to have specialised threat and predator-prey interactions where they can react in far faster speeds, which the authors refer to as higher temporal resolution.

The premise is that the critical flicker fusion frequency (the flicker fusion threshold is defined as "frequency at which an intermittent light stimulus appears to be completely steady to the average human observer.") can be used to measure the temporal resolution of animals when they are facing a predator or threat and must process the information to evade.

Animals with high metabolic rates had the fastest CFFs and could perceive visual information with finer resolution. And it wasn't affected by brain size!

Using this information, you could evolve your humans to have much faster metabolisms (which is probably a natural byproduct of being able to run 40 miles per hour), possibly smaller size, and squeeze out as much temporal resolution as possible to evade on a whim.

You could also combine that with how flies also utilise yet another third ability - specialised sensory-motor circuits that allows them to reorient themselves and immediately evade to navigate in the opposite direction of an impending threat.

If you allow these abilities into your path of evolution, you can be as stupid as you want - your instincts will still save you from your own stupidity.

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Keep in mind that even with improved reaction time the braking distance for 40mph is still four times greater than for 20mph. And even at 20mph it’s not so much about reaction time but more about braking distance. Source: I’m a runner and cyclist and pedestrians (especially with dogs) are brainless half the time. – Michael Mar 22 at 21:19
@Michael Good point, but I think that remains an issue for all objects of all speeds given obstacles, and evading the obstacle successfully means that you don't necessarily have to come to a complete stop. – The Anathema Mar 22 at 21:24
True, evasion only gets harder linearly. However, suddenly changing course while running full speed can be quite hard. If we assume that runners keep the usual 180 steps/minute a single stride at 40 mph (18 m/s) would be 6 m long! So changing course at all could already take 6 m and successfully evading e.g. a 2 m obstacle would probably take several strides. – Michael Mar 22 at 21:37

Let us assume that the increase in speed ability started originating 4 million years ago (basing on evolutionists point of view).

There are two types of people in the society at this point: those who use this ability carefully and have good brain-body coordination and others who are dumb and just run about, bumping into things. The dumb ones in general will act stupidly and die before making any babies. This would mean that their genes of dumbness would start to disappear from the gene pool of the society. The other group of people who are careful and have good brain-body coordination will live longer and have more kids and gradually their genes of better management of this ability will proliferate in the society.

After several thousands of generations, the society in general would become smart about the use of this ability (because they would be the children of smart people who didn't bump into things). Dumb children would still be born occasionally, but they will get themselves killed before they can have babies.

Now let us assume you do not believe in evolution and want a Creationist point of view on the matter.

God created two types of people: smart ones and dumb ones. God wanted to keep the smart ones alive (that's why He made them smart) and wanted the dumb ones to die and suffer (that's why He created them dumb in the first place). With the passage of time, God's will is fulfilled and the smart people proliferate while the generations of dumb ones are slowly wiped off the face of Earth, just as God wanted it to be.


In the end (after several thousand generations), there would only be smart people left who would not be bumping into things and getting themselves killed :) So there would be no problem about the stupid use of this ability.


The normal medical procedures would be used for treating people who bump into things at high speed. The medical procedures we have today are used for treating high speed accidents and concussion damages. The same procedures (possibly more aggressively) could be used for treating high speed collision damages in your world.

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"genes of dumbness" <- EPIC – AndreiROM Mar 22 at 19:37
But you admitted that there will still be dumb people born getting themselves killed. Certainly it would not be a major problem, but it would still exist on occasion, and even smart people will make stupid mistakes, So the question becomes how to deal with the couple of accidents a year that result due to this. – Ryan Mar 22 at 19:41
The Darwin Awards were created for a reason, namely taking ones self out of the gene pool. – Pᴀᴜʟsᴛᴇʀ2 Mar 22 at 20:17
Haven't you seen Idiocracy?! ;-) – Karl Gjertsen Mar 23 at 14:50

Note: the question implies that since great speed still can cause fatality, the human body structure isn't different, and thus, I haven't considered the deeper effects, such as differences in technology or biology.

If 40 mph (which equals to 64 kph) would be the final limit of human capability, then we have no much fear, since as usual, only a very small percentage of people can reach the top 10%.

I'd assume an 1.6 multiplier since the current final limit is around 40 km/h - this means that, or at least I think we can also assume safely that the average comfortable running speed would also increase - this is now 10-25 km/h. In your world, that'd be 16-40 km/h.

Either way, the matter is that on higher numbers, not only death, but general injuries are also more common. Think of falling in soccer.

What I can predict is a slight increase in medical traffic, because of the increased amount of such injuries. Also, protective wears (on knees, head, elbows and such) would be much more popular and more widely used. You may also consider different fences and walls on lots, e.g. in prisons, because with higher speed, you can also jump higher.

To answer your question: improved medical care, and protection can, but not surely will decrease the chance and the amount of fatal injuries.

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I think you're on to something, but only scratching the surface. The human body would not look the same way, and our technology, etc. would be different as well. – AndreiROM Mar 22 at 19:41
@AndreiROM given the fact that 64 km/h might be lethal to people, I assumed that the details are less important here, and that the question implies there's no change in human body structure. – Zoltán Schmidt Mar 22 at 20:07

Putting aside the obvious that has been stated before by others - this wouldn't happen and if it did, would be solved through evolution - there are a few things you could do to prevent deaths.

  • Helmets and HANS devices

Helmets currently used by motorcyclists would prevent a good lot of head/brain trauma in the event of a person-on-person collision. Of course, 40 mph head on is still going to be pretty much fatal with just a helmet, so you'd have to hope they slowed down a little before impact. A special brace known as a HANS device would help prevent neck injuries in the associated crash. (

  • Crumple Zones

Sounds silly, but this is something your people would need to factor into their daily attire. In my head, those big novelty sumo suits would probably be helpful, but restrictive. So they'll be safe, but might struggle to reach 40.

  • Active crash avoidance

We're starting to see this in cars, a radar that catches incoming objects and alerts a driver or to some extent takes control of a vehicle to prevent a crash. It could be achieved in a similar manner, Nippon in Japan (among others) have been doing research into 'steering' people using low frequencies pumped into their ears ( Just have everyone wear their helmets with special radar/steering input, and like birds they'll appear to "magically" steer away from one another.

Obviously human error will be the biggest killer here, but with a few safety devices you can have a reduced risk population that's also a massive laugh to watch going about their lives.

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Dumb people would be fine. Even dumb people learn very quickly not to put their hands in the blender, their heads in the oven or their junk in the vacuum cleaner. Well, most of them at least.

Just because you can run 40 mph doesn't mean you will, you'll still walk to the coffee machine at 1 mph, walk down the road at 2 mph, and only speed up to a full sprint when you can see there is no obstacles in your path.

However, on the road, I can see people running alongside cars on the road, and you'd expect them to speed up or slow down with the (light) traffic, but generally follow the same rules we have for driving today - except they would behave a lot like cyclists do today, running red lights and ignoring junctions. I expect they'd wear the same protective gear for running as cyclists do (hopefully not the lycra though) and end up causing the same amount of accidents, though potentially being more manoeuvrable to avoid some of them that cyclists don't have. As everyone could run without having to get a bike, we'd see far more people running than we do currently cycling so the car traffic would be significantly less, only for those carrying loads, being lazy, or wanting to go even faster on main roads.

Still almost nobody would run into walls, or run into other people - run on a standard side of the road would solve that. Running cross traffic, well, that'd happen regularly. Maybe we'd fine each participant, or tag them with ball and chains for a time so they had to walk!

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Nothing really changes: lack of exercise is still #1 killer.

To fully consider the safety issues, we need to consider what changes in terms of acceleration, stopping distance and so on. I consider the case where sudden ability to reach 40mph on their own steam is due to "bicycles" popping up all over cities. There isn't much point in the government taking bicycles off people, since anyone with a bolt cutter and five seconds is easily able to acquire another. These "bicycles" may look like the following:

Photo By Petit Brun from France - Braddley Wiggins et Jean Christophe Péraud, CC BY-SA 2.0

Since people aren't any stronger, the rate of acceleration isn't increased, just the top speed. It takes time, effort and perhaps even a bit of a downhill stretch to reach 40mph. On the other hand, since the human body isn't any stronger it is not any more able to withstand impact than in our world. To stop idiots killing them selves, the government may

  1. Fine "cyclists" that don't wear helmets.
  2. Fine "cyclists" that don't have lights at night.
  3. Promote "cycling" as being healthy.

I imagine (3) would be quite effective at ensuring that idiots see this "cycling" business as far too much work. If they stay at home and clog their arteries with fast food instead then at least they won't endanger the lives of others. Interestingly, those wearing helmets may actually be at greater risk. In any case, lack of exercise would kill 400 times as many people as cycling.

I have only considered one case of how human might "run" at 40 mph without anything government regulated device. However 40 mph running works in your world, if it takes time, effort and exercise to reach the top speed of 40 mph, lack of exercise may well be still be the #1 killer. 40 mph running may in fact reduce total deaths.

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I would say that you answered your own question with: "Let's assume that humans can run 40 mph and the human body can handle it."

As one evolves to be able to run at those speeds, other evolutionary traits would likely take place for these traits to become common. Higher density of the skeletal structure, or even exoskeletal structures potentially. Perhaps even higher density and more prevalent fat stores that would cushion such blows.

Depending on the ease of running at 40 mph, would people be driving as often still? If I could run 40 mph, and say the adaptation of this has made it so that doing so doesn't wind us very much, I'd probably just run to a lot of places that I drive to now.

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If I could run at 40mph, I wouldn't have a car. Anything that isn't in running distance would be much better to reach by train, especially since I can run to or from the train station in no time. In a city, I would outrun any car easily. – gnasher729 Mar 24 at 0:04
Haha yeah well - that depends a lot on where you live. I live just outside of Detroit and we are very car-centric, with virtually no public transportation. But generally, I would agree with you. – Jesse Williams Mar 24 at 13:36

Obviously this is a problem, as it's not a car but an ability the government can't just take it away.

Of course the government can! Just require a license to operate (your legs) on public roadways, like a car or motorcycle license.

If you are caught violating traffic law, Police could still "pull you over" and cite you. I'm sure that they would require that you wear a helmet or other protective gear and possess some pricey insurance policy.

As for running into walls, you could get fined for destruction of property I suppose, but that wouldn't be the biggest of your worries I'm guessing.

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There already pretty good answers (Even Mine is a great one!). It's a glorified comment to add a few points.

1. Economics

Food One side effect of a entire population running around is calories needs increase. This makes land even more valuable and food production even a bigger business.

Oil Car and other vehicles can still be necessary for long distances depending of how much a human can endure to run at top speed. Cargo vehicles like trains and ships are still common. Anyway oil consumption will decrease a bit an can even not be biggest business around.

Shoes A interesting side effect can be high demand for footwear. Running at 40 mph all day ill make people buy running shoes weekly. Footwear industry can be a lot larger in this hypothetical world.

2 Culture

WAR Running at 40 mph a platoon trained to run carrying heavy logs can crush gates and break enemy lines with easy. All tactics can change since mobility is a key factor since the first pre historian tribal skirmishes. At that speed spearmen and javelins throwers can be fearsome.

Streets Since cars are more a utility for cargo and long trips streets ill be build for fast running people. That means maybe a grass lane with a damn good drain system.

Transit Law enforcement in transit ill don't need the arise of automobile or the big confluence of horse powered wagons. Each ancient civilization ill create his transit code and in modern days we ill got specialized transit lawyers.

Alcohol can be strict prohibited for everyone!

Communication Even in medieval eras communication ill be a lot better between tows and feuds. Also depending on human endurance trips can be a lot more common increasing trade letting people in touch that with the mobility of armies and the need for more land can even "enlarge" a lot the size of the small medieval feuds and nations ill be likely to form early.

3 Science

Need is the mother of invention That's true so steam power => Combustion => Aviation can arise a bit later for example but A increased commnucated humanity can need telegraph early.

Now trying to respond the question:

How to keep stupid people alive

Biology Just make a better peripheral vision. the human ability to drive at 40 mph proves we don't need a lot more upgrades.

Mobile Phones Can strict prohibited to move and use a mobile device for obvious reasons. In some places they can be entirely banned.

Alcohol Prohibited since ancient times! Can even be a taboo

Sorry for the lack of beer & wine guys.

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Everyone at the very least would some sort of head protection, even the stupid people.

This wouldn't be for safety per say, but primarily to stop bugs and rocks impacting on your face all the time and so you could keep your eyes open to see where you are going.

With everyone wearing helmets, helmet manufacturers would compete for safety features adding in parachutes/airbags etc. keeping all people alive.

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Even motorcycles don't come with parachutes or airbags in the real world. The market for them when you have to carry their entire weight on your back / belt is going to be vanishingly small. Or, for parachutes, still the same BASE-jumpers. – Peter Cordes Mar 23 at 9:27

Surprised that nobody made an answer of the top-voted comment, but it needs to be said.

This is exactly the kind of situation that Natural Selection helps out in. If there were suddenly a situation where a sizable percentage of humans were not capable of protecting themselves from death, the traits that help humans avoid that would have a lot of selection pressure on them. Eventually, those traits would become almost universal.

The next generation may not be a whole lot smarter, but it will certainly be better at not killing itself by running into/in front of things.

To put it in Darwin Award terminology, your "stupid people" will take care of the problem for us by removing themselves from the Gene Pool.

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I don't necessarily agree with this, but in Guns, Germs, & Steel, Jared Diamond made an unsupported argument that modern society protects people from their own stupidity so much that people from less advanced societies are now noticeably smarter. – T.E.D. Mar 23 at 18:26
Because as a joke and a comment it works, but it's not quite enough for a full answer ;) – Separatrix Mar 23 at 18:34
@user16295 - Well, next time you need someone with diarrhea of the fingers to turn your succinct joke into a "full answer", give me a shout. :-) – T.E.D. Mar 23 at 19:09


Since culture adapts more quickly than biology, springs will be encouraged, a la the 90's videogame carmageddon.

enter image description here

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Animals that can move faster tend to have bigger eyes that can see further clearly, so I'd expect this to start evolution toward people with bigger eyes also.

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